Methods of forming a gate stack that is void of silicon clusters within a metallic silicide film thereof

Abstract

A method for forming a gate stack which minimizes or eliminates damage to the gate dielectric layer and/or silicon substrate during the gate stack formation by the reduction of the temperature during formation. The temperature reduction prevents the formation of silicon clusters within the metallic silicide film in the gate stack which has been found to cause damage during the gate etch step. The present invention also includes methods for dispersing silicon clusters prior to the gate etch step.

1. A method of forming a gate stack, comprising:
 forming a gate dielectric layer on a silicon substrate;  
 forming a polysilicon layer on top of the gate dielectric layer;  
 subjecting the polysilicon layer to an ion implantation of impurities;  
 depositing a metallic silicide film in a non-annealed state atop the polysilicon layer; and  
 depositing a dielectric cap layer formed from silicon nitride over the metallic silicide film at a temperature below about 600° C., wherein the temperature is sufficiently low to maintain the metallic silicide film in the non-annealed state.  
 
   
   
     2. The method of  claim 1 , wherein depositing the dielectric cap layer formed from silicon nitride over the metallic silicide film is effected at a temperature of between 400° C. and 600° C. 
   
   
     3. The method of  claim 1 , wherein depositing the dielectric cap layer formed from silicon nitride over the metallic silicide film is effected at a temperature of about 500° C. 
   
   
     4. The method of  claim 1 , wherein depositing the dielectric cap layer formed from silicon nitride over the metallic silicide film is effected at a temperature sufficiently low to preclude formation of silicon clusters in the metallic silicide film. 
   
   
     5. A method of forming a gate stack, comprising:
 forming a gate dielectric layer on a silicon substrate;  
 forming a polysilicon layer on top of the gate dielectric layer;  
 subjecting the polysilicon layer to an ion implantation of impurities;  
 depositing a metallic silicide film in a non-annealed state atop the polysilicon layer; and  
 depositing a dielectric cap layer formed from silicon nitride over the metallic silicide film at a temperature below about 600° C., wherein the temperature is sufficiently low to preclude formation of silicon clusters in the metallic silicide film.  
 
   
   
     6. The method of  claim 5 , wherein depositing the dielectric cap layer formed from silicon nitride over the metallic silicide film is effected at a temperature of between 400° C. and 600° C. 
   
   
     7. The method of  claim 5 , wherein depositing the dielectric cap layer formed from silicon nitride over the metallic silicide film is effected at a temperature of about 500° C. 
   
   
     8. A method for forming a gate stack, comprising:
 providing a semiconductor substrate with a dielectric layer on an active surface of the semiconductor substrate, wherein a polysilicon layer is disposed over the dielectric layer;  
 forming a metallic silicide film in a non-annealed state over the polysilicon layer;  
 forming a dielectric cap from silicon nitride on the metallic suicide film at a sufficiently low temperature so that the metallic silicide film remains in the non-annealed state;  
 forming and patterning a resist layer on the dielectric cap;  
 etching the dielectric cap, the metallic silicide film, and the polysilicon layer; and  
 stripping the resist layer.  
 
   
   
     9. The method of  claim 8 , wherein forming the dielectric cap is effected at a temperature below about 600° C. 
   
   
     10. The method of  claim 8 , wherein forming the dielectric cap from silicon nitride on the metallic silicide film is effected at a temperature of between 400° C. and 600° C. 
   
   
     11. The method of  claim 8 , wherein forming the dielectric cap from silicon nitride on the metallic silicide film is effected at a temperature of about 500° C. 
   
   
     12. The method of  claim 8 , wherein forming the dielectric cap from silicon nitride on the metallic silicide film is effected at a temperature sufficiently low to preclude formation of silicon clusters in the metallic silicide film.